1. Field of the Invention
The present invention relates to a polarizing illumination device for uniformly illuminating a rectangular illumination area and the like by using polarized lights polarized in the same direction, and to a projector using the polarizing illumination device. More particularly, the present invention relates to a structural technique for synthesizing light emitted from two light source sections while unifying the directions of polarization of the light.
2. Description of Related Art
A liquid crystal display device using a modulation device of a type that modulates a specific polarized light, such as a liquid crystal device, can utilize only one of two types of polarized light components included in light emitted from a light source. Therefore, there is a need to enhance light utilization efficiency in order to obtain a bright projection image. Since a projector using only one light source has a limited ability to enhance light utilization efficiency, however, the amount of light has been increased by using a plurality of light sources as a way to obtain a bright image.
When simply a plurality of light sources are arranged, however, the angle distribution of light for illuminating an illumination area is increased (the illumination angle is increased). Therefore, the amount of light in a given illumination angle is the same as that in the case where only one single light source is used. Consequently, in a projector in which the illumination angle is controlled by a projection system, the amount of light is not practically increased even when a plurality of light sources are used.
In addition, even if the amount of light is increased by using a plurality of light sources, when only one of two types of polarized light components, which are included in light emitted from the light sources, can be used, and half the light is wasted, which reduces the effectiveness by half.
It is an object of the present invention to provide a polarizing illumination device that is able to utilize both polarized light components by using a plurality of light sources, without increasing the illumination angle, and to provide a projector that is able to project a considerably bright projection image.
In order to achieve the above object, according to the present invention, there is provided a polarizing illumination device including:
first and second light source sections;
a polarization-separating-and-synthesizing optical element having a first polarizing separation film for transmitting, of light emitted from the first light source section, a linear polarized light polarized in a direction parallel to an incident surface thereof and reflecting a linear polarized light polarized in a direction perpendicular to the incident surface, and a second polarizing separation film for transmitting, of light emitted from the second light source section, a linear polarized light polarized in a direction perpendicular to an incident surface thereof and reflecting a linear polarized light polarized in a direction parallel to the incident surface;
a first condensing-and-reflecting optical element including a plurality of condensing-and-reflecting devices for approximately reversing the direction of travel of the linear polarized light transmitted by the first polarizing separation film and forming focal images;
a second condensing-and-reflecting optical element including a plurality of condensing-and-reflecting devices for approximately reversing the directions of travel of the linear polarized lights reflected by the first polarizing separation film and the second polarizing separation film and forming focal images;
a third condensing-and-reflecting optical element including a plurality condensing-and-reflecting optical devices for approximately reversing the direction of travel of the linear polarized light transmitted by the second polarizing separation film and forming focal images;
a first polarization-state conversion optical element disposed between the polarization-separating-and-synthesizing optical element and the first condensing-and-reflecting optical element;
a second polarization-state conversion optical element disposed between the polarization-separating-and-synthesizing optical element and the second condensing-and-reflecting optical element;
a third polarization-state conversion optical element disposed between the polarization-separating-and-synthesizing optical element and the third condensing-and-reflecting optical element; and
a polarization conversion optical element for unifying the directions of travel of linear polarized lights synthesized by the polarization-separating-and-synthesizing optical element;
wherein an approximately central axis of a luminous flux, which is reflected by the condensing-and-reflecting devices of the first condensing-and-reflecting optical element and the third condensing-and-reflecting optical element and enters the polarization conversion optical element, and an approximately central axis of a luminous flux, which is reflected by the condensing-and-reflecting devices of the second condensing-and-reflecting optical element and enters the polarization conversion optical element, are not parallel to each other, and do not overlap.
The construction of the polarizing illumination device of the present invention will be described more in detail as follows.
Firstly, of the light polarized in random directions (hereinafter, referred to as xe2x80x9crandomly polarized lightxe2x80x9d) that is emitted from the first light source section, the linear polarized light polarized in the direction parallel to an incident surface thereof passes through the first polarization separation film, and the linear polarized light polarized in the direction perpendicular to the incident surface is reflected by the first polarizing separation film. On the other hand, of the polarized light emitted from the second light source section, the linear polarized light polarized in the direction perpendicular to the incident surface thereof passes through the second polarizing separation film, and the linear polarized light polarized in the direction parallel to the incident surface is reflected by the second polarizing separation film. Here, xe2x80x9cincident surfacexe2x80x9d is a technical term used in the field of optics, and relates to a virtual plane including an approximately central axis of a luminous flux entering a film and a normal line to the film.
The linear polarized light, which passes through the first polarizing separation film, passes through the first polarization-state conversion optical element, is reflected by the first condensing-and-reflecting optical element, passes through the first polarization-state conversion optical element again, and travels toward the polarization-separating-and-synthesizing optical element. In this case, this light is divided by the first condensing-and-reflecting optical element into a plurality of intermediate luminous fluxes to pass through the first polarization-state conversion optical element two times, whereby it is converted into a linear polarized light polarized in a different direction by about 90 degrees. Therefore, when the light returns to the polarization-separating-and-synthesizing optical element, it is reflected by the first polarizing separation film, and travels toward the polarization conversion optical element. The polarized light that travels toward the polarization conversion optical element in this way is designated as a first polarized luminous flux.
The linear polarized lights, which are reflected by the first polarizing separation film and by the second polarizing separation film, pass through the second polarization-state conversion optical element, are reflected by the second condensing-and-reflecting optical element, pass through the second polarization-state conversion optical element again, and travel toward the polarization-separating-and-synthesizing optical element. In this case, each of the light is divided by the second condensing-and-reflecting optical element into a plurality of intermediate luminous fluxes to pass the second polarization-state conversion optical element two times, whereby it is converted into a linear polarized light polarized in a different direction by about 90 degrees. Therefore, when the light returns to the polarization-separating-and-synthesizing optical element, it passes through the first and second polarizing separation films, and travels toward the polarization conversion optical element. The polarized light that travels toward the polarization conversion optical element in this way is a polarized light polarized in a direction perpendicular to the first polarized luminous flux. This is designated as a second luminous flux.
The linear polarized light, which passes through the second polarizing separation film, passes through the third polarization-state conversion optical element, is reflected by the third condensing-and-reflecting optical element, passes the third polarization-state conversion optical element again, and travels toward the polarization-separating-and-synthesizing optical element. In this case, the light is divided by the third condensing-and-reflecting optical element into a plurality of intermediate luminous fluxes to pass the third polarization-state conversion optical element two times, whereby it is converted into a linear polarized light polarized in a different direction by about 90 degrees. Therefore, when the light returns to the polarization-separating-and-synthesizing optical element, it is reflected by the second polarizing separation film, and travels toward the polarization conversion optical element. This polarized light is polarized in the same direction as the first polarized luminous flux. Therefore, this polarized light is also designated as a first polarized luminous flux.
The first and second polarized luminous fluxes each including a plurality of intermediate luminous fluxes form a plurality of focal images on the polarization conversion optical element or in the vicinity thereof. Here, an approximately central axis of the first polarized luminous flux and an approximately central axis of the second polarized luminous flux are not parallel to each other, and do not overlap. Therefore, the focal images of the first polarized luminous flux and the focal images of the second polarized luminous flux are formed at positions different from each other. Therefore, the direction of polarization of the first polarized luminous flux and the direction of polarization of the second polarized luminous flux can be unified by the polarization conversion optical element.
With the construction as described above, according to the polarizing illumination device of the present invention, although the two light source sections are used, an area to be illuminated can be equalized to an area to be illuminated by almost one light source section without increasing an incident angle (illumination angle) of illumination light with respect to the illumination area. For this reason, since the amount of light per given illumination angle can be made double that in the case where a single light source section is used, it is possible to illuminate the illumination area very brightly. In addition, since the intermediate luminous fluxes formed by the respective condensing-and-reflecting optical elements are superposed on one illumination area, it is possible to illuminate uniformly the illumination area. Therefore, if the polarizing illumination device of the present invention is used as a light source of a display device, a projection image having extremely uniform brightness can be obtained. Furthermore, according to the polarizing illumination device of the present invention, the randomly polarized lights emitted from the first and second light source sections can be synthesized into one type of polarized light without causing any loss. Therefore, if the polarizing illumination device of the present invention is adopted in a display device using a modulation device of a type that modulates a specific polarized light, such as a liquid crystal device, it is possible to obtain an extremely bright projection image.
The positions where the first to third condensing-and-reflecting optical elements are formed, in this nature, are not clearly defined. In short, the first to third condensing-and-reflecting optical elements may be disposed so that a plurality of focal images formed by the first polarized luminous flux and a plurality of focal images formed by the second polarized luminous flux do not overlap each other on the polarization conversion optical element.
In the present invention, an opening shape of each of the condensing-and-reflecting devices can be made similar to the shape of an illumination area. Since light from the light source sections is divided by the condensing-and-reflecting optical elements into a plurality of intermediate luminous fluxes, and finally superposed on the illumination area, the adoption of the above construction can guide the light from the light source sections to the illumination area most efficiently.
In the present invention, a condensing optical element including a plurality of condensing devices is disposed on the side of an incident surface or on the side of an emitting surface of the polarization conversion optical element, in order to condense light emitted from the polarization-separating-and-synthesizing optical element. The disposition of the condensing optical element in this way makes it possible to guide effectively the plurality of intermediate luminous fluxes formed by the condensing-and-reflecting optical elements to predetermined positions of the polarization conversion element while condensing the luminous fluxes. Therefore, an advantage is provided that the polarization conversion efficiency can be increased. When the first to third condensing-and-reflecting optical elements are composed of different numbers of condensing-and-reflecting devices, the condensing optical element may be composed of at least as many condensing devices, or twice as many condensing devices as the number of condensing-and-reflecting devices that constitute the condensing-and-reflecting optical element having the largest number of condensing-and-reflecting devices. However, if the light utilization efficiency of the condensing optical element is regarded as important, the latter construction may preferably be adopted.
In the present invention, a superimposing optical element for superimposing light emitted from the polarization conversion optical element on the illumination area can be disposed on the side of the emitting surface of the polarization conversion optical element. The disposition of the superimposing optical element in this way makes it possible to guide effectively the plurality of intermediate luminous fluxes formed by the condensing-and-reflecting optical elements to the illumination area. Therefore, an advantage is provided that the illumination efficiency can be improved.
In the present invention, an optical-path-changing optical element for changing an optical path of light emitted from the polarization conversion optical element can be disposed on the side of the emitting surface of the polarization conversion optical element. If the optical-path-changing optical element is disposed so that illumination light can be emitted in a direction parallel to a plane defined by optical axes of two light source sections, the thickness of the polarizing illumination device in one direction can be reduced, and a low-profile polarizing illumination device can be realized. Therefore, when the polarizing illumination device is used as a light source of a projector or the like, a compact projector can also be obtained.
In the present invention, each of the condensing-and-reflecting devices of the first to third condensing-and-reflecting optical elements can be formed of a plurality of curved-surface reflecting mirrors. In addition, each of the condensing-and-reflecting devices of the first to third condensing-and-reflecting optical elements can be composed of a lens, and a reflecting surface provided on a surface of the lens opposite to the polarization-separating-and-synthesizing optical element. With this construction, light from the light source sections can be easily divided into a plurality of intermediate luminous fluxes. Here, if the curved-surface reflecting mirrors are formed of decentering mirrors, or if the lens is formed of a decentering lens, the above-described polarization conversion optical element and the condensing optical element can be reduced in size, and the light can be effectively guided to the illumination area without using the above-described superimposing optical element.
The polarizing illumination device according to the present invention can be used in a projector having an optical modulation device for modulating light emitted from the polarizing illumination device, and a projection optical system for projecting the light modulated by the optical modulation device.
Furthermore, the polarizing illumination device according to the present invention can be used in a projector which has a color-light-separating optical element for separating light emitted from the polarizing illumination device into a plurality of colors of light, a plurality of optical modulation devices for modulating each of the colors of light separated by the color-light-separating optical element, a color-light-synthesizing optical element for synthesizing the light modulated by the plurality of optical modulation devices, and a projection optical system for projecting the light synthesized by the color-light-synthesizing optical element, and which can display a color image.
In addition, the polarizing illumination device according to the present invention an be used in a projector having a reflective optical modulation device for modulating light emitted from the polarizing illumination device, a polarization-separating optical element for separating a plurality of polarized light components included in the light emitted from the polarizing illumination device and the light modulated by the reflective optical modulation device, and a projection optical system for projecting the light modulated by the reflective optical modulation device and emitted via the polarization-separating optical element.
Furthermore, the polarizing illumination device according to the present invention can be used in a projector which has a plurality of reflective optical modulation devices for modulating light emitted from the polarizing illumination device, a polarization-separating optical element for separating a plurality of polarized light components included in the light emitted from the polarizing illumination device and the light modulated by the plurality of reflective optical modulation devices, a color-light-separating-and-synthesizing optical element disposed between the polarization-separating optical element and the plurality of reflective optical modulation devices, for separating light emitted from the polarizing illumination device into a plurality of colors of light and synthesizing the colors of light emitted from the plurality of reflective optical modulation devices, and a projection optical system for projecting the light modulated by the reflective optical modulation devices and emitted via the color-light-separating-and-synthesizing optical element and the polarization-separating optical element, and which can display a color image.
In addition, the polarizing illumination device according to the present invention can be used in a projector which has a color-light-separating optical element for separating light emitted from the polarizing illumination device into a plurality of colors of light, a plurality of reflective optical modulation devices for modulating each of colors of light separated by the color-light-separating optical element, a plurality of polarization-separating optical elements for separating a plurality of polarized light components included in each of the colors of light separated by the color-light-separating optical element and in each of the colors of light modulated by the plurality of reflective optical modulation devices, a color-light-synthesizing optical element for synthesizing the light modulated by each of the reflective optical modulation devices and emitted via each of the polarization-separating optical element, and a projection optical system for projecting the light synthesized by the color-light-synthesizing optical element, and which can display a color image.
In this way, when a projector using the polarizing illumination device of the present invention, a bright, and uniformly bright projection image can be obtained. Since the polarizing illumination device of the present invention emits luminous fluxes polarized in the same direction, it is suitable for a projector using liquid crystal devices as optical modulation devices.
In the above-described projector, at least one of the first and second light source sections may preferably be detachably constructed. With this construction, one of the light source sections can be detached when the projector is carried, thereby improving portability.
In addition, in the above-described projector, at least one of the first and second light source sections may preferably be selectively lit. With this construction, for example, when the projector is driven by a battery, the longevity of the battery can be extended by selectively lighting only one of the light sources. In addition, the brightness of a projection image can be appropriately changed according to the environment, or according to the preferences of the viewer such that two light source sections are lit when the projection image is viewed in a light place, and only one of them is selectively lit when the projection image is viewed in a dark place.
Furthermore, in the above-described projector, spectral characteristics and brightness characteristics of light emitted from the first and second light source sections can be allowed to differ from each other. With this construction, the hue of the illumination light can be easily set to a predetermined hue.